In the field of wireless networks, a base station regularly transmits a beacon as a control packet. When a mobile terminal moves into the reaching area of the beacon, the mobile terminal receives the beacon and detects that the mobile terminal has entered an area where the mobile terminal can communicate with the base station. In a communication using a base station, mobile terminals which have received beacons all perform communications via the base station.
In addition, there is an ad-hoc wireless network in which terminals each perform relaying, thereby enabling communications of data between each relay terminal and a terminal which is present within a certain area around the relay terminal, without using a base station. In the ad-hoc wireless network, a terminal to perform relaying is not specified, which is different from the communication using a base station. Therefore, when communicating data between two terminals, it is necessary to specify, as a relay terminal, a terminal which is suitable for a relay with respect to a communication between the two terminals. Methods of exchanging control information for specifying a relay terminal are classified into a proactive method (for example, see Non-Patent Documents 1 and 2) in which control information is periodically exchanged, and a reactive method (for example, see Non-Patent Documents 3 and 4) in which control information is exchanged when starting a data communication. Generally, it is said that the proactive method is effective when the moving speed of a terminal is slow, and that the reactive method is effective when the moving speed of a terminal is fast.